Green’s Dictionary of Slang

toot n.⁵

(N.Z.) the buttocks; the anus.

2003

McGill Reed Dict. of N.Z. Sl. 215: toot The bum. Multiple possibilities for its origin, as in the noise it can emit, the Maori name tutae for excrement, the Australian contraction of toilet, the dog-French toute suite [...] The popular phrase a root up the toot could be a kick in the bum or anal intromission of the penis.

In phrases

a root up the toot (n.)

a kick in the behind; an act of sodomy.

2003

see sense 1 above.